The invention relates to an arrangement for feeding air in a supercharged piston engine, which air feeding arrangement comprises at least a supercharging device arranged for feeding air to more than one cylinder, an air chamber in connection with the supercharging device, and a channel arrangement leading from the air chamber to each cylinder of the piston engine.
The invention also relates to a method of operating a supercharged piston engine, in which method combustion air is fed by means of a supercharging device at a pressure higher than ambient pressure into an air chamber in connection with the supercharging device, and air is led from the air chamber to cylinders in connection with the air chamber through channel arrangements between the cylinders and the air chamber.
It is known that pressure vibrations take place in intake channels or passages of piston engines and various solutions for damping intake noise have been disclosed. In publication DE 19641715 there is shown a resonator connected in parallel with an inlet air channel. The resonator is provided with a connection tube having variable length and diameter. In this kind of solution a starting point is to attenuate noise emitted from the intake channel to the environment. However, this fails to handle possible pressure pulsations in the engine itself. On the other hand, various resonator arrangements in connection with naturally aspirated engines for enhancing gas admission into the cylinder or combustion chamber have been suggested, e.g. U.S. Pat. No. 5,572,966. In contrast to naturally aspirated engines, in supercharged engines it is possible to select the boost pressure. Thus, a desired amount of gas mixture on average may be fed into the cylinders, but unevenness of charge of the cylinders still remains as a problem due to pressure pulsations.
Additionally, in supercharged multi-cylinder piston engines some problematic operating disturbances, e.g. the so-called pumping phenomenon, have been noticed. In the pumping phenomenon pressure pulsation moves the operating point of the supercharger repeatedly over to the surging area. In certain types of engines valves operate in groups, causing strong pulsation in the air chamber, impeding the operation of the supercharger and so adversely affecting the operation of the engine.
Moreover, the pulsation of pressure in the air chamber has an adverse effect on the filling of the cylinders. That is because the pressure level in the vicinity of each inlet valve fluctuates, and the amount of air remaining in the cylinder is ruled by the local pressure level when the inlet valve closes. The local pressure level may vary considerably, specifically in supercharged engines.
It is found that specifically in supercharged engines applying the so called Miller-process, the valve timing, specifically when closing the inlet valve in the cycle prior to bottom dead center, and also on simultaneous opening of valves, aggravates the above mentioned pumping phenomena.
It is an aim of the present invention to provide an arrangement for feeding air into a piston engine and a method of operating a supercharged piston engine, with which it is possible to advance the known art and minimize the above and preferably other shortcomings of the prior art. It is a specific intention of the invention to provide an arrangement suitable for feeding air into a piston engine applying the so-called Miller-process and a method of operating such a piston engine.
The present invention provides an arrangement for feeding air in a supercharged piston engine and a method of operating a supercharged piston engine.
The arrangement for feeding air in a supercharged piston engine according to the invention comprises at least a supercharging device arranged for feeding air to more than one cylinder, an air chamber in connection with the supercharging device, and a channel arrangement leading from the air chamber to each cylinder of the piston engine. According to the invention a resonator system is arranged in connection with the air chamber for attenuating pressure pulsation in the air chamber. Advantageously the resonator system is arranged mainly to attenuate pressure pulsation, which appear at the third harmonics of the rotational speed of the engine or frequencies below that. The resonator system may be formed by use of a resonator chamber, which opens into the air chamber of the engine.
Preferably the supercharging device is connected to a first end of the air chamber and the resonator system is arranged to operate substantially on the opposite end, i.e. a second end, to the first end of the air chamber. This way the effect of the resonator system according to the invention is optimal.
According to an embodiment of the invention the resonator system may be formed of one or several elements each defining an elongated space, which are arranged to open into the air chamber. The air chamber is arranged to have a certain cross-sectional area perpendicular to a direction of successive cylinders, which in this connection means an average area. The average cross sectional area may be obtained by dividing the total volume of the air chamber by its total length. It is noticed that, in practice, it is advantageous as a whole that the cross sectional area of the space of the resonator system is below 50%, but advantageously below about 30%, of the cross-sectional area of the air chamber.
The resonator system provides advantages relating to its construction and production if it is arranged in connection with constructions of an engine block and/or an air chamber.
The resonator system may also comprise a mechanical oscillator as well as an actuator system for moving the oscillator.
In the method according to the invention in connection with a supercharged piston engine, combustion air is fed by means of a supercharging device to a pressure higher than ambient pressure into an air chamber in connection with the supercharging device, and air is led from the air chamber to cylinders in connection with the air chamber through channel arrangements between the cylinders and the air chamber. A pressure pulsation is generated in the air chamber, which pulsation is half-wavelength shifted from a pulsation in the air chamber at the third harmonics of the rotational speed of the engine or at frequencies below that. Advantageously but not necessarily, the pressure pulsation is formed mainly at the opposite end to the coupling location of the supercharging device in the air chamber.
The resonator system may be controlled to be adjusting according to the rotational speed of the engine. If so, at each respective speed, the resonator system is controlled to attenuate substantially that pressure pulsation which appears at the third harmonics of the rotational speed of the engine or frequencies below that, so it always operates optimally.
Advantageously the engine is arranged to be operated according to the so-called Miller-process and the supercharging device operates using the energy of exhaust gases of the engine.